This invention relates to firefighting, and particularly to the use of potassium formate as a freeze point depressant in fire hydrants.
In northern climates, a difficult problem for firefighters has been the tendency of the water in fire hydrants to freeze. Frozen water either in the hydrant itself or in the working parts of the valves which operate it may completely prevent use of the hydrant, frustrating any timely efforts to thaw the hydrant or otherwise release the water upstream from the hydrant, thereby risking loss of life and costly destruction of property.
In recent years, a common approach to this problem has been to add one or more glycols to the water in the fire hydrant, and sometimes in the pipe segments near the hydrant valves as well. This has been successful to some degree, but glycols have a tendency to degrade, and some of them are toxic. In addition, glycols can be metabolized by microorganisms under certain conditions, creating foul smells and resulting in decreased effectiveness as a freeze point depressant.
In addition, hydrants are periodically checked for performance, necessitating a release of the contained fluid to the environment. Glycols have an additional disadvantage in that there may be regulatory and liability consequences to their release to the environment. It is highly undesirable for ethylene glycol to find its way into drinking water. Disposal of water containing glycols can be particularly difficult where hundreds of hydrants may be routinely emptied and refilled in a community.
Potassium formate has been suggested for use in solution as a heat transfer medium, as in cooling systems. See Example 2 of David F. Smith""s U.S. Pat. No. 2,233,185, and Kardos et al U.S. Pat. No. 5,104,562, which discusses the freeze point of a saturated solution of potassium formate. See also Minks et al U.S. Pat. No. 6,059,996. Gavlin et al, in U.S. Pat. No. 5,853,458, propose the use of potassium formate as a solvent ingredient together with glycols.
Potassium formate was also suggested, in U.S. Pat. No. 5,993,875, to be useful for lowering the freeze point of brines used for preserving fish.
We are not aware, however, of the use of potassium formate in a fire hydrant maintenance system.